Ski binding

ABSTRACT

An improved ski binding engages the sole-plate of a boot assembly at three mutually-spaced locations. Cooperating concave and convex members are operatively interposed between the ski and the sole-plate at two transversely-spaced forward locations. The engagement of a plunger in a release cam provides the third longitudinally-spaced location at the rear end of the sole-plate. The plunger is biased by a spring stack having variable force-todisplacement characteristics in successive force ranges. During separation of the boot assembly from the ski, the sole-plate is permitted to pivot about at least one of the locations.

United States Patent 1191 Moog et al.

1 1 Nov. 25, 1975 1 SKI BINDING [75] Inventors: William C. Moog. East Aurora.

N.Y.; Alfred J. Mastropole, Saddle River, NJ.

[73] Assignee: Moog 1nc., East Aurora. NY.

[221 Filed: May 3, 1974 [21] Appl. No.: 466,528

[52] US. Cl... 280/1135 K; 267/162. 280/1135 T (51] Int. Cl. A63C 9/086 [58] Field ofSearch... 280/1135 K, 1 1.35 C,11.35 D,

280/11.35 E. 11.35 A. 11.35 R. 11.35 T;-

[561 References Cited UNITED STATES PATENTS 3.010.713 11/1961 Turkovich 267/162 3.258.274 6/1966 Beecher 280/1135 T 3.630.538 12/1971 Klein et a1. 280/1 1.35 T

3.731.944 5/1973 Salomon 280/1135 C 3.771.806 11/1973 Hinterholzer et a1. 280/1135 D 3.779.570 12/1973 Betschart, .lr......,, 280/1135 R 3.797844 3/1974 Smblka 280/1135 C 3.825.273 7/1974 Greene 280/1135 K 3.838.866 10/1974 DAles'sio... 280/1 135 K FOREIGN PATENTS OR APPLICATIONS 44 /767 1965 Japan 280/1135 R 1.233.690 1960 France 280/1135 C Primary Examiner-David Schonberg Assislanl E.raminer-David M, Mitchell Attorney. Agent, or FirmSommer & Sommer [57I ABSTRACT An improved ski binding engages the sole-plate of a boot assembly at three mutually-spaced locations. C0- operating concave and convex members are operatively interposed between the ski and the sole-plate at two transversely-spaced forward locations. The engagement of a plunger in a release cam provides the third longitudinally'spaced location at the rear end of the sole-plate. The plunger is biased by a spring stack having variable f0rce-todisplacement characteristics in successive force ranges, During separation of the boot assembly from the ski. the sole-plate is permitted to pivot about at least one of the locations.

21 Claims. 13 Drawing Figures U.S. Patent Nov. 25, 1975 Sheet 1 of3 3,921,995

wwww my Aw/ OV.

US Patent Nov. 25, 1975 Sheet 2 of3 3,921,995

US Patent Nov. 25, 1975 Sheet3of3 3,921,995

m CHARACTERISTIC FORCE vs. DEFLECTION CURVE g T LL Li] D z MAX. PLUNGER FORCE AQ/ICONVENT'ONAL SPR'NG 5E MOOGSPRING T I I PRELOAD Q I A w B FORCE 3| 4 II I m 5' gg I 4g. .72 I rw In 4| 2 I a E a I 0: Lu 5| I E u FI B I w L LLII I 'I 95 3 g 0 WORKING E I RANGE I I PLUNGER DEFLECTION 3, EFFECT OF SKI BENDING 0N RELEASE SETTING II 0 w 2% i CONVENTIONAL con. SPRING z MAX. PLUNGER FoRcE No: MOOG SPRING 5 I I I B I I IS I I I I?? 15 UJ 1% I :2 n: gl I 2 5' I I u: g I I I :5 I I I I 3 SKI BENDING WORKING I EFFEcT RANGE I I PLUNGER DEFLECTION -P- SKI BINDING BACKGROUND OF THE INVENTION l. Field of the Invention The present invention relates generally to ski bindings for releasably securing a boot assembly to a ski, ans particularly to such bindings for a boot assembly having a sole-plate arranged beneath the boot.

2. Description of the Prior Art The bro d concept of securing a sole-plate to a boot and thereafter releasably securing such boot assembly to a ski is known, and structure embodying such con cept is shown in each of the following patents:

Fend Pat. No. 3,752,491 discloses a boot assembly having a full length sole-plate secured to a ski. The boot assembly is engaged at three longitudinally spaced aligned locations and is arranged to rest on a plurality of bearing blocks mounted on the ski. While capable of yaw and forward pitch releases, Fends binding appears to be incapable of separating from the ski in the event of a backward pitch release.

Rumaner Pat. No. 3,284,092 teaches the provision of a boot assembly having a heel-plate which may separate from the ski in either a forward or backward pitch direction, but not in a yaw direction.

Additional details of other prior art structures may be found in Hatlapa U.S. Pat. No. 3,244,431, Wiley U.S. Pat. Nov 3,504,992, and Wick U.S. Pat No. 3,359,010,

SUMMARY OF THE INVENTION The present invention relates to a ski binding wherein the improvement includes holding means operatively interposed between a ski and a boot assembly at three mutually-spaced locations for releasably holding the boot assembly to the ski and for permitting the boot assembly to pivot about at least one of the locations during separation of the boot assembly from the ski in any direction away from the ski. In the preferred embodiment, the boot assembly includes a sole-plate secured to a boot.

The holding means includes first means arranged to exert a first force on the boot assembly at a first location, second means arranged to exert a second force on the boot assembly at a second location spaced laterally from the first location in a direction transverse to the longitudinal centerline of the ski, and third means arranged to exert a third force on the boot assembly at a third location spaced longitudinally from the first and second locations. The third force opposes the first and second forces. The holding means may support the boot assembly in spaced relation to the upper surface of the ski.

In a preferred embodiment, the first and second locations are arranged on opposite sides of the longitudinal centerline of the ski proximate that portion of the boot assembly which is arranged beneath the metatarsal head bone of the boot wearers foot. The first and second means may severally have a convex member, such as the spherical head of a ball stud, mounted on the sole-plate and a concave member mounted on the ski and arranged to be engaged by the convex member. Each concave member may have a ball-receiving surface arranged to urge its engaged ball head laterally outwardly in a direction transverse to the center-line so as jointly to urge the boot assembly toward a centered position on the ski,

The third means may include a cam member mounted on the sole-plate and a forwardly-acting plunger member mounted on the ski. In the preferred embodiment, the cam member has an elliptical con- 5 cave surface arranged to be engaged by the plunger member and to disengage therefrom upon substantial relative permissible movement thcrebetween in any direction normal to the centerline. The cam surface may be arranged to permit such disengagement more readily in the yaw direction of its major axis than in the pitch direction of its minor axis.

The plunger member may include a housing mounted on the ski, a plunger slidably mounted on the housing, and spring means arranged to act between the housing and plunger for urging the plunger toward the cam member. The spring means has a relatively high forceto-displacement relationship in a first force range. and a relatively low force-to-displacement relationship in a second force range. When the plunger is normally en gaged in the cam member, the spring means is displaced to the substantial threshold of the second force range. In the preferred embodiment, the spring means includes a stack of Belleville springs.

Accordingly, one object of the present invention is to provide an improved ski binding wherein forces are applied to the boot assembly at three mutually-spaced locations.

Another object is to provide an improved ski binding wherein a boot assembly is permitted to pivotally release from a ski in any direction away from the ski.

Another object is to provide an improved ski binding wherein a boot assembly is arranged to separate from a ski upon application ofa predetermined release torque.

Another object is to provide a safety ski binding wherein a boot assembly is arranged to separate from a ski before injury may occur to a skier.

Another object is to provide an improved plunger member which includes spring means having a relatively high force-to-displacement relationship in a first force range and a relatively low force-todisplacement relationship in a second force range.

Still another object is to provide an improved release cam for use in a ski binding, which cam is configured to disengage from a plunger more readily in a yaw direction than in a pitch direction.

These and other objects and advantages will become apparent from the foregoing and ongoing specification which includes the drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a top plan view of the inventive ski binding shown mounted on a fragmentary portion of a ski and illustrating holding means at three locations and, at a forward one of which, portions of the binding are broken away to depict more clearly specific details of the engagement of one convex member with its concave member constituting one of the forward holding means.

FIG. 2 is a vertical longitudinal sectional view thereof, taken on line 22 of FIG. I, and illustrating fragmentary portions of the boot heel and toe in association with the binding and further illustrating the concave and convex members of the other of the forward holding means in cross-section.

FIG. 3 is a side elevational view of the binding depicted in FIG. 1, as viewed in the same direction as FIG. 2, and showing fragmentary portions of the heel and toe of the boot secured to the sole-plate.

FIG. 4 is an enlarged fragmentary vertical longitudinal sectional view of the plunger member. taken on line 44 of FIG. I. and showing the nose of the plunger normally engaged with the release cam.

FIG. 5 is a fragmentary vertical transverse sectional view of the ski. taken on line 55 of FIG. 4, and showing a rear elevational view of the plunger member.

FIG. 6 is a fragmentary vertical transverse sectional view of the plunger member. taken on line 6-6 of FIG. 4.

FIG. 7 is an enlarged exploded perspective view of the two transversely-spaced concave members and the forward pair of transversely spaced convex members. such pairs of concave and convex members when cooperatively engaged. comprising the forward components of the holding means.

FIG. 8 is an enlarged fragmentary vertical transverse sectional view of the binding. taken generally on line 88 of FIG. 3, and showing a rear elevational view of the cam member with the plunger removed.

FIG. 9 is a further enlarged fragmentary vertical longitudinal sectional view of the binding. taken on line 9-9 of FIG. 8, illustrating the cross-sectional shape of the cam member in the direction of its minor axis.

FIG. [0 is a further enlarged fragmentary horizontal sectional view of the binding. taken on line l0l0 of FIG. 8, and showing the cross-sectional configuration of the cam member in the direction of its major axis and further illustrating the socket surface and tangential lateral surfaces thereof.

FIG. I1 is a greatly enlarged fragmentary vertical sectional view of a bearing button carried by the sole plate. this view taken on line llll of FIG. 1.

FIG. I2 is a force-displacement curve for a particular stack of Belleville springs and illustrating the point of plunger preload deflection and the working range.

FIG. 13 is another force-displacement curve for the particular stack of Belleville springs and further illustrating the effect of ski bending on the plunger member.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 and 3, the inventive ski binding. generally indicated at 18, is shown mounted on the platnar horizontal upper surface 19 of a fragmentary portion of a horizontally elongated ski 20 having a planar horizontal lower working surface ZI. a leftward front end (not shown). and a rightward rear end (not shown). The ski binding connects the ski to a boot assembly 22. As shown. this boot assembly includes a boot 23 worn by the skier and a sole-plate 24 suitably secured thereto.

The inventive binding 18 is shown as comprising holding means operatively interposed between ski 20 and sole-plate 24 at three mutually-spaced locations for releasably holding the sole-plate to the ski and for permitting the sole-plate to pivot about at least one of the locations during separation of the sole-plate from the ski in any directon away from the ski. As best shown in FIG. I. the holding means includes first means 25 an ranged to exert a first force on the sole-plate at a first location. second means 26 arranged to exert a second force on the sole-plate at a second location spaced laterally from the first location in a direction transverse to the longitudinal centerline of the ski. and third means 28 arranged to exert a third force on the sole-plate at a third location spaced longitudinally from the first and second locations to oppose the first and second forces.

In FIG. I, sole-plate 24 is shown it being a horizontally elongated plate-like member lLli ing 1| forward portion 29 extending rearwardly from its rounded vertical front end face 30 for about onethird of its longitudinal extent, a transversely widened intermediate portion 31 continuing reurivmdly for about uitc t .velltii of such longitudinal extent. and a rearward portion 32 continuing rearwardly and accounting for the balance of such longitudinal extent and terminating at the trans verse planar vertical rear end face 33 of the sole-plate. While the intermediate portion 31 is shown as having a transverse dimension extending substantially the full width of the ski. the forward and rearward portions 29. 32, respectively. may have a transverse dimension of about seven-eighths of such width. Sole-plate 24 is also shown as having vertical left and right sides 34, 35. respeetively. severally including the corresponding verti cal sides of the forward. intermediate. and rearward portions.

As best shown in FIG. 1, sole-plate 24 has a substantially planar horizontal top surface 36 provided with a plurality of transversely-Spacedlongitudinally-extending flutes or grooves 38. In FIGS. 2 and 3, the bottom surface of the sole-plate is shown as being configured at various levels with respect to top surface 36 to provide the forward sole-plate portion 29 with a vertically thickened part 39, the intermediate sole-plate portion 31 with a greater vertically thickened part 40 spaced longitudinally from part 39, and the rearward sole-plate portion 32 with an elongated vertically thickened part 41 and to the rear thereof with a greater verticallythickened part 42 proximate rear end face 33. The bottom surface of the sole-plate also defines a pair of transversely-spaced recesses 43 arranged between parts 39 and 40, which recesses extend inwardly from the left and right sides 34, 35, respectively, of the soleplate for a purpose later described. A plurality of longitudinally spaced-internally-threaded horizontal transverse holes 44 are shown provided in each of thickened parts 39 and 41 to receive the threaded horizontal inturned end portions 45 of four L-shaped rods 46.

Referring to FIGS. 2 and 3, the ski boot 23 is a conventional one having arcuate toe and heel grooves 49, and which may be arranged to have its bottom or sole 51 engage the upper surface 36 of the sole-plate. The toe portion of boot 23 is shown secured to the soleplate by a flexible steel cable 52 having its arcuate intermediate portion arranged in toe groove 49 and a knurled turnbuckle 53 at each of its free ends suitably threaded onto the corresponding one of forwardly and upwardly inclined legs 54 of one pair of rods 46 engaged in holes 44 provided in forward part 39. The heel portion of the boot is similarly secured to the sole-plate by a flexible steel cable 55 having its arcuate intermediate portion arranged in heel groove 50 and a knurled turnbuckle S6 at each of its free ends suitably threaded onto the corresponding one of upwardly and rearwardly inclined legs 54 of the other pair of rods 46 engaged in holes 44 provided in part 41. If desired, one or both of cables 52, 55 may additionally be provided with a suitable toggle-type locking lever (not shown) to facilitate engagement and disengagement of the cables with the boot. By adjusting the extent to which the hori zontal inturned end portion 45 of each L-shaped rod 46 is threaded into its hole 44, the boot may be inclined in a horizontal plane with respect to the longitudinal centerline of the sole-plate to compensate for a toe-in or toe-out orthopedic problem ofa particular skier. Moreover, the horizontal inturned end portions 45 of rods 46 may be suitably threaded into any of the longitudinallyspaced holes 44 to accommodate any size or length of ski boot within a predetermined range. Accordingly, cables 52, 55 may be employed to secure the boot to the sole-plate and to prevent their unintended separation. even during a fall of the skier which may cause the boot assembly to separate or release from the ski.

Sole-plate 24 is further shown provided with a pair of transversely-spaced internally-threaded horizontal holes 58 extending into the intermediate thickened part 40 from recesses 43, which holes 58 are shown inclined rearwardly and inwardly for convenience in manufacturing to imaginarily converge at the center of the release cam at rear location 28.

Referring to FIGS. 1, 2 and 7, the first and second means 25, 26 severally include a convex member 59. mounted on the sole-plate and a concave member 60 fixed to the ski through a intermediate rectangular horizontal base plate 57. The convex members 59 are shown as being ball-studs having their externally threaded shank portions 59' suitably threaded into holes 58 and having their spherical ball head surfaces 61 arranged forwardly in recesses 43 proximate that part of the boot which is arranged beneath the metatarsal head bone of a skiers foot. Alternatively. the shank or stud portions of the convex members may be pressfitted into holes provided in the sole-plate. As best shown in FIG. 7, each concave member 60 is shown as including a forward mounting portion 62 provided with a pair of longitudinally-spaced vertical through holes 63 (FIG. 2) through which a pair of screw fasteners 67 are passed and suitably engaged in the ski. and a rearward vertically-thickened portion 64 provided with a rearwardly facing concave receiving surface 65 arranged to be engaged by one of spherically surfaced convex members 59. Each of ball receiving surfaces 65 is partcylindrical and inclined inwardly and rearwardly with respect to the longitudinal centerline of the ski and is defined by the intersection of vertically-thickened por tion 64 with a cylindrical surface having an outwardly and forwardly-extending horizontal axis inclined in a horizontal plane at an acute included angle of about with respect to a horizontal line arranged perpendicularly to a vertical plane including the longitudinal centerline of the sole-plate. Moreover, each of surfaces 65 is bounded by an upper edge or lip 66 to resist a backward pitch release and has a slightly upwardly inclined generally C-shaped cross-sectional shape in a normal plane taken midway between its inner and outer sides 68, 69, respectively, such that a line bisecting the inscribed arc of the surface in such plane will be vertically inclined at an imaginary acute included angle of about 12 with respect to the horizontal upper surface 19 of the ski. Each of surfaces 65 is provided with the inwardly and rearwardly directed inclination to urge its engaged convex member laterally outwardly in a direction generally transverse to the longitudinal centerline of the ski. Should the intermediate portion 31 of the sole-plate 24 experience lateral movement in a horizontal plane with respect to the ski. one of ball heads 61 will ride up the inward and rearward inclination of its engaged receiving surface and be stopped to provide a pivot for horizontal rotation of the sole-plate. If such relative rotational movement does not result in separation of the sole-plate from the ski. inclined surfaces 65 6 will cooperate to urge their engaged ball heads back toward a centered position with respect to the longitudinal centerline of the ski.

An inverted generally L-shaped member 70 is shown mounted on the sole-plate proximate the rear end 33 thereof and includes vertical and horizontal leg portions 71, 72, respectively. As best shown in FIGS. 4 and 8, the vertical leg portion 71 has a forward planar verti cal surface 73 arranged to abut the vertical rear end face 33 of the sole-plate and has a rearwardly facing vertical cylindrical surface 74 having its rotational axis located on the longitudinal centerline of the ski proximate the forward convex surfaces 61. The horizontal upper leg portion 72 is shown as including a pair of lateral rearwardly and inwardly inclined planar vertical surfaces 75 which, at their rearmost ends, join arcuate surface 74; a planar horizontal upper surface 76; a planar horizontal lower surface 78 arranged to abut the upper surface 36 of the sole-plate 24; and an upwardly and rearwardly inclined concave forward surface 79. so configured to accommodate the rounded shape of the heel of the ski boot. A pair of Allen-head bolts 80 are shown arranged in a pair of transversely-spaced countersunk vertical through holes 81 provided in the horizontal leg portion 72 and threadedly engaged in a pair of aligned vertical holes 82 provided in the sole-plate to secure member 70 to the sole-plate.

The third means 28 is shown as including a cam member 83 provided on member 70. and plunger means 84 mounted on the ski through an intermediate rectangular base plate 77 and arranged to engage the cam member. As best illustrated in FIGS. 8-10, cam member 83 is shown as being that portion of member 70 which provides a concave release cam surface extending into a central portion of vertical leg portion 71 from rear cylindrically segmented surface 74. In FIG. 8, the entire release cam surface 83 is shown as presenting an elliptical outline, when viewed in rear elevation, having a horizontal major axis and a vertical minor axis. The point of intersection of the major and minor axes of the release cam is specifically shown as being in the vertical plane also including the longitudinal centerline of the sole-plate.

Within its elliptical outline. the release cam 83 includes a central concave socket surface 83' and a pair of crescent-shaped lateral surfaces 83" which extend outwardly from socket surface 83' in the direction of the major axis. Socket surface 83 is configured as a vertically elongated elliptical portion ofa spherical surface having a spherical radius R (FIGS. 9 and 10). Specifically, the socket surface occupies a shperical are of about 120 in the direction of the vertical minor axis of the outline of the cam member 83 (FIG. 9). and a spherical arc of about 60 in the direction of the horizontal major axis of this cam member outline (FIG. 10). The crescent-shaped lateral surfaces 83" continue tangentially outwardly from the elliptical boundary of the socket surface to intersect cylindrical surface 74 and therewith define the elliptical outline of cam member 83.

Still referring to FIG. 8, member 70 is shown as also including an upwardly and rearwardly inclined flat separation surface 85 joining the cylindrical surface 74 and the lower planar horizontal surface 86 of vertical leg portion 71. When viewed in rear elevation, surface 85 presents an inverted parabolic outline defined by the intersection of its plane with cylindrically-segmented surface 74.

In FIG. 4, plunger means 84 is shown as generally including a housing 88 mounted on the ski. a plunger 89 slidably mounted on the housing for horizontal movement. and spring means 90 arranged to act between the housing and the plunger for urging the plunger forwardly toward cam member 83.

Housing 88 includes a horizontally elongated tubular block-shaped member 91 having a pair of lower longitudinally-elongated integral attaching flanges 92 extending outwardly from the vertical sides of the housing and severally provided with a pair of longitudinallyspaced vertical through holes 93. and an annular end plug member 94 engaged in the open rear end of the body member. The body member 91 is shown secured to the ski by a plurality of screw fasteners 95 arranged in holes 93 to act on the upper surfaces of flanges 92 and suitably engaged in the ski. Body member 91 is further shown as having an internal longitudinally-extending stepped cylindrical throughbore bounded by a relatively large diameter cylindrical surface 96 extending forwardly from the vertical rear surfaces 98 of the body member, a rearwardly-facing annular vertical shoulder 99, and a smaller diameter concentric cylindrical surface 100 continuing forwardly through the vertical front end wall 101 of the body member. A thin-walled cylindrical sleeve bushing 102 of a low friction material, preferably teflon. is shown as lining cylindrical surface 100 to facilitage sliding movement of plunger 89 relative to body member 91.

The end plug member 94 has a forwardly projecting cylindrical portion shown externally threaded at 103 to engage an internally threaded portion 104 of body cylindrical surface 96, and four diagonally arranged rearwardly extending rectangular bosses or lugs 105 between which a suitable tool (not shown) may be inserted to rotate the end plug member with respect to the body member. The end plug member 94 is further provided with a central concentric horizontal throughopening bounded by cylindrical wall surface 106.

Plunger 89 is shown as having a longitudinally-elon gated stepped cylindrical outer surface including a forward cylindrical peripheral surface 108 extending rearwardly from the vertical front end face 109 of the plunger, a rearwardly-facing annular vertical shoulder 110, and a rearward smaller diameter cylindrical peripheral surface 111 continuing rearwardly from shoulder and terminating at the vertical rear end face 112 of the plunger. Plunger 89 is further provided with an internally-threaded axial through-bore 113. A hemispherical ball stud has its externally threaded shank portion 114 screwed into the forward portion of bore 113 so as to have the rearwardly-facing annular vertical surface 115 of its forwardly-rounded hemispherical head or nose 116 snugly engage the front end surface 109 of the plunger through an intermediate pair of flat washers 118 which function as shims. Hence. by varying the number of washers 118, the effective length of the plunger may be easily varied.

A tubular screw 119 has its shank portion 119' externally threaded and screwed into the rear portion of bore 113 so as to have the forwardly-facing annular vertical surface 120 of its cylindrically-enlarged head 121 at the rear end of the shank abut the rear end surface 112 of plunger 89. an annular marginal portion of head 121 is shown extending radially beyond the smaller diameter cylindrical surface 113 of plunger 89. The vertical rear end face of screw head 121 is shown as having a pair of radially disposed recesses 119" to 8 receive a suitable tool, such as a spanner wrench (not shown), for turning this end plug relative to the body of plunger 89. The rear end of the bore of tubular screw 119 is shown closed by a button-like closure 117 having a stem 117' which is frictionally held in this bore.

Plunger 89 is slidably mounted in housing 84 so as to have its forward cylindrical surface 108 arranged in and slidably engaging bushing 102, and its rearward cylindrical surface 111 arranged within the larger diamter chamber of the body member and surrounded by the internal cylindrical surface 106 of end plug member 94.

A ring 122 made of a low friction material. such as teflon. is carried by the rear end of plunger 89 and con fined thereon by screw 119. This ring 122 has an outer cylindrical surface 123 arranged to slidably engage internal cylindrical surface 106 of end plug member 94, and has an internal cylindrical surface 124 arranged to engage the cylindrical surface 111 of plunger 89, a rearwardly-facing annular vertical inner shoulder 125 arranged to abut forward surface 120 of the marginal portion of head 121, and a larger diameter internal cy' lindrical surface 125' arranged to surround the periphery of head 121. Preferably as shown a stationary low friction sleeve bushing 102 similar to bushing 102, is suitably provided on surface 106 of the end plug member 94 to further facilitate low friction sliding of the plunger 89 within the end plug 94 of housing 88.

In the particular embodiment illustrated. the spring means 90 are shown as including a stack of twenty Belleville washers or springs 126 arranged in ten pairs of two each and arranged to act against the annular shoulder or abutment surface 110 of plunger 89 through an intermediate flat washer 128 and against the forward annular vertical face or stop surface 129 of end plug member 94 and/or forward annular vertical face or abutment surface 130 of plunger ring 122 through a pair of intermediate flat washers 131, 131. Thus. the plunger 89 and the Belleville spring means 90 constitute an assembly unit which may be removed from housing 88. An elastomeric O-ring 132 is arranged between forward washer 128 and body member shoulder 99 to serve as a resilient bumper. Since the housing 88 is fixed to the ski. the stack of Belleville springs 126 will act on plunger shoulder 110 to continuously urge plunger 89 forwardly toward cam member 83. However, since one principal advantage of a Belleville spring stack lies in the ease by which different force-to-displacement charactistics may be obtained by varying the number or configuration of such springs, the present invention contemplates that the size and configuration of springs 126 and the number and grouping of the springs into a spring stack, may be varied to obtain the particular force-to-deflection characteristics desired.

As best shown in FIGS. 4 and S, a rectangular vertical plate 133 provided with a large diameter central opening is secured between body member 91 and end plug member 94 and has a right ear portion 134 provided with a vertically-elongated slot 135 to receive one end of a runaway strap or cable 136. The other end of cable 136 is suitably attached to the boot assembly to prevent the ski from sliding downhill of the skier in the event that a fall of the skier should cause the boot assembly to separate from the ski.

Referring to FIGS. 1, 2 and 11, a pair of bearing buttons 138 are arranged in a pair of transversely-spaced vertical through holes 139 provided in the rear thickened part 42 of the sole-plate 24. The lower portion of each hole is internally threaded as indicated at 139. As best shown in FIG. 11, each bearing button is a onepiece member including an upper externally-threaded head portion 140 suitably engaged with threaded hole portion 139'. an intermediate neck portion 141 of reduced thickness to render it flexible. and a lower foot or base portion having its flat bottom surface covered with a coating 143 of low friction material, such as teflon. At its upper surface. the bearing button is shown provided with a horizontal diametral slot 144 into which the blade of a suitable tool (not shown) may be inserted to rotate the bearing button realtive to the sole-plate. Desirably. the bearing buttons are arranged in holes 139 such that the lower coated surfaces 143 will extend downwardly beyond the lower surface of the sole-plate but spaced from the upper surface of base plate 77, thereby maintaining the normal threepoint suspension of the sole-plate.

Should a force cause the rear end of the sole-plate 24 to move vertically downwardly. the lower coated surfaces 143 of the foot portions 142 will engage the upper surface of the base plate 77 to provide a stop for such movement. At the same time. the foot portions 142 will be permitted to pivot by flexing the neck portions 141 to insure full area contact between coated surface 143 and the upper surface of the base plate. While such downward bottoming force may produce a relatively high pressure on the small surface area of coated surfaces 143, it is known that the coefficient of friction of tefion is inversely related to applied pressure. Accordingly. buttons 138 serve to provide a stop for such bottoming movement of the sole-plate and further provide a low friction engagement between such bottomed sole-plate and the base plate to permit low friction lateral relative movement therebetween in the event of a yaw release. While the preferred embodiment has been described as including bearing buttons 138, the present invention further contemplates that the operative engagement between the cam and plunger members may be suitably designed to support the rear end of the soleplate above the ski in slightly spaced relation thereto, as indicated at 86' in FIG. 4. under most conditions of downward force. Bearing buttons 138 may be omitted since the possibility of frictional contact between the ski and sole-plate is unlikely so as to hinder a yaw release.

As best illustrated in FIG. 4, the convex hemispherical nose 116 of the plunger is arranged to normally engage the area of the central socket surface 83 of release cam surface 83. While the plunger engages the release cam in area contact when plunger nose 116 is centrally seated on socket surface 83, any relative movement between the plunger and the heel portion of the sole-plate in any direction normal to the longitudinal centerline of the ski will result in off-center point contact between the plunger nose and the release cam. At any such offcenter point, the release cam surface will exert an opposing force on the nose of the plunger, which force will have a rearwardly acting longitudinal component urging the plunger to withdraw into the housing, and another component urging the plunger back toward its centered engagement with socket surface 83'. Accordingly, should such relative movement be insufficient to cause the plunger to disengage from the cam member. the unique configuration of the release cam surface will always urge the nose of the plunger back toward its normal centered position with socket surface 83'. It will be apparent to those skilled in this art that such relative sliding or exercising" move ment between the engaged cam and plunger members will represent energy manifested by the forces encountered while skiing and that such energy will be absorbed by compressive deflection of the spring stack and further dampened by the frictional engagement between adjacent Belleville washers of the spring stack. Hence. the inventive binding possesses a high energy absorption capability prior to disengagement of the cam and plunger members.

From a comparison of FIGS. 9 and 10. it will be apparent that the plunger nose 116 must displace rearwardly a greater distance to disengage from the release cam 83 in the direction of the vertical minor axis than in the direction of the horizontal major axis. Moreover. the crescent-shaped lateral surfaces 83" of the release cam act as inclined planes and provide the release cam with a lesser rearward slope in a lateral direction than in a vertical direction. Accordingly, the release cam operates to favor, or more easily permit. disengagement of the plunger nose from the release cam in a horizontal yaw direction than in a vertical pitch direction.

It should be further apparent that in the event of a forward pitch release wherein the sole-plate pivots about balls 61 and the release cam 83 is moved vertically upwardly to disengage from the plunger nose 116, the latter will thereafter engage and ride on the separation surface 85. To secure the boot assembly to the ski. the skier first attaches the sole-plate to the boot by means of toe and heel cables 52, 55. Thereafter. the skier may pitch the sole-plate forwardly to engage each of convex members 59 into its cooperative concave member 60 and move the heel of the sole-plate downwardly. such motion causing plunger nose 116 to ride up separation surface 85 and engage release cam member 83.

The unique operation of plunger means 84 may be best understood by viewing the structure of such plunger means (FIG. 4) in connection with the curves depicted in FIGS. 12 and 13, such curves illustrating the force-to-displacement characteristics of the spring means 90.

When the nose 116 of the plunger 89 is normally engaged in area contact with the central socket surface 83 of the release cam, spring means 90 will compressed between end plug member 94 and plunger shoulder to point A (FIG. 12) to bias the plunger forwardly with a preload force corresponding to such compressive displacement.

Unlike a conventional coil spring which may typically have a linear spring rate or force-to-displacement relationship within its operating range. the stack of Belleville springs 126 has a non-linear force-to-displacement relationship within its operating range. The variable spring rate of the Belleville spring curve is herein defined as the slope ofa line tangential to any point on its force-to-displacement curve. such slope being approximating the incremental force required to produce a related displacement. In viewing the spring rate curves of FIGS. 12 and 13, it will be noted that within a first force range. bounded at its upper end by the preload force at point A. the tangential slope of the spring rate at any point of the curve is greater than at any point in a second successive force range having the preload force at point A as its lower limit. Accordingly. the spring means has a first relatively high force-to-displaeement relationship in the first force range and a relatively low foree-to-displacement relationship in the second force 1 1 range. It is to be noted that within the second force range. a relatively small additional increment of force will produce a relatively large increment of additional plunger displacement.

The extent of displacement required for separation of the boot assembly including sole-plate 24 from ski 22 is indicated at point B in FIGS. 12 and 13. The extent of plunger displacement between points A and B in FIG. 12 is the working range of the plunger and represents engagement of the plunger nose with various points on the cam surface 83. It is to be noted that only a relatively small increment of additional force in the second force range is needed to displace the plunger through the working range of the spring stack.

In reality. the front and rear ends of the ski may bend upwardly in a plane normal to its upper surface 19. The effect of such bending is to shorten the distance between concave member 60 and plunger means 84 and cause additional plunger displacement. the effect of bending being represented horizontally from point A to point C in FIG. 13. In conventional ski bindings. the plunger is biased forwardly by a coil spring having a linear spring rate within its operating range such that additional plunger displacement caused by this ski bending effect will produce a proportional incremental increase in biasing force. In the inventive binding. however. the additional plunger displacement attributable to the ski bending effect will produce a smaller incremental force increase. Moreover. the invention contemplates that the ski bending effect may be anticipated. Specifically. the spring means may be designed such that the preload displacement plus the incremental displacement expected due to ski bending will displace the spring stack to the substantial threshold of the second force range. such incremental displacement being represented from point A (nominal preload displacement) to point C (preload displacement plus incremental displacement) in FIG. 13.

It is further desired to design the spring means to permit separation of the boot assembly from the ski in terms of a release torque having an arm distance approximately equal to the longitudinal spacing between the front locations 25, 26 and the rear location 28. Such overcoming release torque may be on the order of 1.000 in-Ibs. in a yaw direction, 2.700 in-lbs. in aa forward pitch direction, and 1.700 in-lbs. in a backward pitch direction. These values of release torque are only exemplary and it may be desired to increase or decrease such values to accommodate the ability ofa particular skier.

In the event of a severe fall of the skier. the plunger will be displaced rearwardly to point B in FIG. 12 or point B in FIG. 13 to permit disengagement of the plunger nose from the release cam and separation of the boot assembly from the ski. Once the plunger nose has been disengaged, the spring means will expand and propel the plunger forwardly, leftwardly as viewed in FIG. 4. As the plunger accelerates forwardly, the forward end of the spring stack. including front washer 128, will engage O-ring 132 and the forward face of the marginal portion of head l2] will engage the shoulder 125 of the ring 122. This ring. slidable relative to end plug 94. will then act on the rear end of the spring stack which will exert a rearward force tending to decelerate the forward movement of the plunger and prevent the forwardly-propelled plunger from impacting on the housing. such deceleration serving to transfer the ki- 12 netic energy of the moving plunger back to the spring stack.

In this manner. the present invention provides improved plunger means 84 for a ski binding adapted to releasably secure a boot assembly to a ski. and having a detent recess 83 arranged on one of the boot assembly and ski. The improved plunger means is mounted on the other of the boot assembly and ski and includes: a housing 88; a plunger 89 slidably mounted on the housing and arranged to engage the recess; and Belleville spring means 90 arranged to act between the housing and plunger to urge the plunger toward the recess. The Belleville spring means has a force-to-displacement relationship represented by a curve (FIG. 12) including a portion (identified as the working range" in FIG. 12) of such low slope that a relatively small additional increment of force within this portion produces a relatively large increment of displacement of the Belle ville spring means. When the plunger is normally engaged in the recess. the Belleville spring means is displaced to the substantial threshold (point A in FIG. 12) of the low-slope portion. Hence. the Belleville spring means may urge the plunger into engagement with the recess with substantially constant force.

The inventive holding means thus engages the soleplate at three mutually-spaced locations to hold the boot assembly to the ski and to permit the boot assembly to pivot about at least one of the locations during separation of the boot assembly from the ski in any direction away from the ski. The first and second locations are arranged at the points or areas of contact between the concave and convex members of the first and second means 25 and 26, respectively. The third location is arranged at the point or area of contact between the cam and plunger members constituting the third means 28. Since a force acts normal to its point of application. each of the first. second and third forces applied at the first. second and third locations. respectively. may be oblique and have components acting in any three mutually perpendicular directions.

In a pure yaw release. the sole-plate 24 may experience rotative movement in a plane parallel to the upper surface 19 of the ski. The forward portion of the soleplate may rotate in the yaw direction and pivot about the third means 28. Conversely, should the rear portion rotate. the sole-plate may pivot about one of the first and second means 25 and 26. The forward portion of the sole-plate may initially rotate about the third means 28 until one of convex members 25, 26 is stopped by its engaged concave member. Thereafter, if the applied yaw torque is sufficient. continued pivotal rotation of the sole-plate relative to the ski will cause the plunger to disengage from the cam member to permit the boot assembly to separate from the ski. The initial rotative movement of the forward portion of the sole-plate thus functions to absorb and dissipate low energy impulses encountered while skiing.

In a pure pitch release, the sole-plate 24 may experience rotational movement in a vertical plane. Should the third means 28 disengage. the sole-plate will pivot about the first and second means 25 and 26 (forward pitch release) prior to separation. Conversely. if the first and second means should become disengaged, the sole-plate may pivot about the third means (backward pitch release) prior to such disengagement.

In a combined or oblique release having a pitch component and a yaw component. the sole-plate 24 will be permitted to pivot about at least one of the first. second 13 and third means 25, 26 and 28. During this combined release. the plunger is designed to disengage from the cam member at a torque intermediate the forward pitch release torque and the pure yaw release torque.

It will thus be seen that the present invention provides an improved ski binding for releasably securing a boot assembly to a ski, wherein the improvement com prises: resiliently-loaded holding means operatively interposed between the ski and boot assembly for releasably holding the boot assembly in a suspended position above the ski in spaced relation thereto, and for permitting the boot assembly to separate from the ski in any direction away from the ski, the holding means providing the only support for the boot assembly by establishing connection between the boot assembly and ski at only three mutually-spaced locations arranged at the apices of an imaginary triangle. In the preferred embodiment herein disclosed, the three locations are arranged at the apices of an isosceles triangle having the included angle between its two equal sides bisected by the longitudinal centerline of the ski.

in the preferred embodiment herein illustrated and described, the convex members 59 are fixed to the soleplate 24 and the concave members 60 are mounted on the ski 20. However, it is also contemplated that the positions of such members could be reversed to mount the convex members on the ski and the concave members on the sole-plate. Similarly, the cam and plunger members may be alternatively mounted on the ski and soleplate. respectively. Moreover, the holding means need not apply the forces at the exact locations herein described. The spacing and arrangement of such locations may be reversed. varied, or modified, as desired. The various concave and convex members and surfaces need not be spherical. but may include other surfaces as well. Similarly, spring means should not be limited to the size. type, number or orientation expressly described.

As used in the appended claims. the term boot as sembly" should be construed in its broadest sense to include operative structure other than that expressly shown and described. For example, it is contemplated that a boot itself could be provided directly with the necessary surfaces or parts of the various first. second and third means described in the specification without the intermediary of a sole-plate. Such an arrangement is within the scope of the expression boot assembly, as used herein.

While a preferred embodiment of the present invention has been shown and described, it will be understood by persons skilled in this art that various additional changes and modifications may be made without departing from the spirit of the invention which is described in the following claims.

What is claimed is:

l. A ski binding for releasably securing a boot assembly to a ski, wherein the improvement comprises:

resiliently-loaded holding means operatively interposed between said ski and boot assembly for releasably holding said boot assembly in a suspended position above said ski in spaced relation thereto and for permitting said boot assembly to separate from said ski in any direction away from said ski. said holding means providing the only support for said boot assembly on said ski and including at each of only three mutually-spaced locations arranged at the apices of an imaginary triangle a concave surface on one of said boot assembly and ski 14 and a convex surface on the other of said boot assembly and ski and contacting said concave surface.

2. A ski binding as set forth in claim 1 wherein said locations are arranged at the apices of an isosceles triangle having the included angle between its two equal sides bisected by the longitudinal centerline of said ski.

3. A ski binding as set forth in claim 1 wherein said holding means includes first means arranged to exert a first force on said boot assembly at a first location. second means arranged to exert a second force on said boot assembly at a second location, and third means arranged to exert a third force on said boot assembly at a third location.

4. A ski binding as set forth in claim 3 wherein at least one of said first, second and third means is ar ranged proximate that portion of said boot assembly which is arranged beneath the metatarsal head bone of the foot of the wearer of said boot assembly.

5. A ski binding as set forth in claim 3 wherein each of said first, second and third means includes a concave member having said concave surface. and a convex member having said convex surface arranged to engage said concave member.

6. A ski binding as set forth in claim 5 wherein a pair of said concave members severally have their concave surfaces oriented to urge their engaged convex members to move laterally in opposite directions transversely of the longitudinal centerline of said ski. whereby said boot assembly is biased toward a centered position relative to said centerline.

7. A ski binding as set forth in claim 3 wherein one of said first, second and third means comprises a cam member and plunger means including a plunger arranged to engage said cam member and to disengage therefrom upon substantial permissible movement therebetween in any direction normal to the longitudinal centerline of said ski.

8. A ski binding as set forth in claim 7 wherein said cam member includes a concave release cam surface configured to permit said plunger to disengage therefrom more readily in one direction than in another direction.

9. A ski binding as set forth in claim 8 wherein said release cam surface presents an elliptical outline and is configured to permit said plunger to disengage therefrom more readily in the direction ofits major axis than in the direction of its minor axis, said major axis lying generally in the plane of said triangle.

[0. A ski binding as set forth in claim 7 wherein said plunger means further comprises:

a housing;

said plunger being slidably mounted on said housing;

and

Belleville spring means arranged to act between said housing and plunger to urge said plunger toward said cam member. said Belleville spring means having a force-to-displacement relationship represented by a curve including a portion of such low slope that a relatively small additional increment of force within said portion produces a relatively large displacement of said Belleville spring means, said Belleville spring means being displaced, when said plunger is normally engaged in said cam member. to the substantial threshold of said portion;

whereby said Belleville spring means urges said plunger into engagement with said cam member with substantially constant force.

l I. A ski binding as set forth in claim [0 wherein said plunger has a pair of spaced and opposing abutment surfaces. and said Belleville spring means is arranged to act against said surfaces when said plunger is disengaged from said cam member.

12. A ski binding as set forth in claim I] wherein. when said Belleville spring means is engaging both of said abutment surfaces. said Belleville spring means is displaced to a point on said curve such that. when said plunger is engaged with said cam member. said Belleville spring means will be displaced to said substantial threshold.

13. A ski binding as set forth in claim l2 wherein a stop surface is provided on said housing adjacent one of said abutment surfaces. and said stop surface is engaged by said Belleville spring means when said Belleville spring means is displaced to said substantial threshold.

14. A ski binding as set forth in claim 12 wherein said plunger and Belleville spring means constitute an assembly unit which may be removed from said housing.

15. A ski binding as set forth in claim 13 wherein said housing includes a tubular body having an opening through which a part of said plunger may project. and a removable end plug arranged to engage said body and having a face providing said stop surface.

16. In a ski binding for releasably securing a boot assembly to a ski, and having a detent recess arranged on one of said boot assembly and ski, the improvement comprising:

plunger means mounted on the other of said boot assembly and ski and including a housing;

a plunger slidably mounted on said housing and arranged to engage said recess; and

Belleville spring means arranged to act between said housing and plunger to urge said plunger toward said recess, said Belleville spring means having a force-to-displaecment relationship represented by 16 a curve having a portion of such low slope that a relatively small additional increment of force within said portion produces a relatively large displacement of said Belleville spring means. said Belleville spring means being displaced by said plunger and transmitting its load to said plunger. when said plunger is normally engaged in said recess, to the substantial threshold of said portion; whereby said Belleville spring means may urge said plunger into engagement with said recess with substantially constant force.

17. The improvement as set forth in claim [6 wherein said plunger has a pair of spaced and opposing abutment surfaces. and said Belleville spring means is arranged to act against said surfaces when said plunger is disengaged from said recess.

[8. The improvement as set forth in claim [6 wherein, when said Belleville spring means is engaging both of said abutment surfaces, said Belleville spring means is displaced to a point on said curve such that when said plunger is engaged with said recess. said Belleville spring means will be displaced to said substantial threshold.

19. The improvement as set forth in claim 18 wherein a stop surface is provided on said housing adjacent one of said abutment surfaces. and said stop surface is engaged by said Belleville spring means when said Belle ville spring means is displaced to said substantial threshold.

20. The improvement as set forth in claim l8 wherein said plunger and Belleville spring means constitute an assembly unit which may be removed from said housing.

21. The improvement as set forth in claim 19 wherein said housing includes a tubular body having an opening through which a part of said plunger may project, and a removable end plug arranged to engage said body and having a face providing said stop surface.

i i i i it 

1. A ski binding for releasably securing a boot assembly to a ski, wherein the improvement comprises: resiliently-loaded holding means operatively interposed between said ski and boot assembly for releasably holding said boot assembly in a suspended position above said ski in spaced relation thereto and for permitting said boot assembly to separate from said ski in any direction away from said ski, said holding means providing the only support for said boot assembly on said ski and including at each of only three mutually-spaced locations arranged at the apices of an imaginary triangle a concave surface on one of said boot assembly and ski and a convex surface on the other of said boot assembly and ski and contacting said concave surface.
 2. A ski binding as set forth in claim 1 wherein said locations are arranged at the apices of an isosceles triangle having the included angle between its two equal sides bisected by the longitudinal centerline of said ski.
 3. A ski binding as set forth in claim 1 wherein said holding means includes first means arranged to exert a first force on said boot assembly at a first location, second means arranged to exert a second force on said boot assembly at a second location, and third means arranged to exert a third force on said boot assembly at a third location.
 4. A ski binding as set forth in claim 3 wherein at least one of said first, second and third means is arranged proximate that portion of said boot assembly which is arranged beneath the metatarsal head bone of the foot of the wearer of said boot assembly.
 5. A ski binding as set forth in claim 3 wherein each of said first, second and third means includes a concave member having said concave surface, and a convex member having said convex surface arranged to engage said concave member.
 6. A ski binding as set forth in claim 5 wherein a pair of said concave members severally have their concave surfaces oriented to urge their engaged convex members to move laterally in opposite directions transversely of the longitudinal centerline of said ski, whereby said boot assembly is biased toward a centered position relative to said centerline.
 7. A ski binding as set forth in claim 3 wherein one of said first, second and third means comprises a cam member and plunger means including a plunger arranged to engage said cam member and to disengage therefrom upon substantial permissible movement therebetween in any direction normal to the longitudinal centerline of said ski.
 8. A ski binding as set forth in claim 7 wherein said cam member includes a concave release cam surface configured to permit said plunger to disengage therefrom more readily in one direction than in another direction.
 9. A ski binding as set forth in claim 8 wherein said release cam surface presents an elliptical outline and is configured to permit said plunger to disengage therefrom more readily in the direction of its major axis than in the direction of its minor axis, said major axis lying generally in the plane of said triangle.
 10. A ski binding as set forth in claim 7 wherein said plunger means further comprises: a housing; said plunger being slidably mounted on said housing; and Belleville spring means arranged to act between said housing and plunger to urge said plunger toward said cam member, said Belleville spring means having a force-to-displacement relationship represented by a curve including a portion of such low slope that a relatively small additional increment of force within said portion produces a relatively large displacement of said Belleville spring means, said Belleville spring means being displaced, when said plunger is normally engaged in said cam member, to the substantial threshold of said portion; whereby said Belleville spring means urges said plunger into engagement with said cam member with substantially constant force.
 11. A ski binding as set forth in claim 10 wherein said plunger has a pair of spaced and opposing abutment surfaces, and said Belleville spring means is arranged to act against said surfaces when said plunger is disengaged from said cam member.
 12. A ski binding as set forth in claim 11 wherein, when said Belleville spring means is engaging both of said abutment surfaces, said Belleville spring means is displaced to a point on said curve such that, when said plunger is engaged with said cam member, said Belleville spring means will be displaced to said substantial threshold.
 13. A ski binding as set forth in claim 12 wherein a stop surface is provided on said housing adjacent one of said abutment surfaces, and said stop surface is engaged by said Belleville spring means when said Belleville spring means is displaced to said substantial threshold.
 14. A ski binding as set forth in claim 12 wherein said plunger and Belleville spring means constitute an assembly unit which may be removed from said housing.
 15. A ski binding as set forth in claim 13 wherein said housing includes a tubular body having an opening through which a part of said plunger may project, and a removable end plug arranged to engage said body and having a face providing said stop surface.
 16. In a ski binding for releasably securing a boot assembly to a ski, and having a detent recess arranged on one of said boot Assembly and ski, the improvement comprising: plunger means mounted on the other of said boot assembly and ski and including a housing; a plunger slidably mounted on said housing and arranged to engage said recess; and Belleville spring means arranged to act between said housing and plunger to urge said plunger toward said recess, said Belleville spring means having a force-to-displacement relationship represented by a curve having a portion of such low slope that a relatively small additional increment of force within said portion produces a relatively large displacement of said Belleville spring means, said Belleville spring means being displaced by said plunger and transmitting its load to said plunger, when said plunger is normally engaged in said recess, to the substantial threshold of said portion; whereby said Belleville spring means may urge said plunger into engagement with said recess with substantially constant force.
 17. The improvement as set forth in claim 16 wherein said plunger has a pair of spaced and opposing abutment surfaces, and said Belleville spring means is arranged to act against said surfaces when said plunger is disengaged from said recess.
 18. The improvement as set forth in claim 16 wherein, when said Belleville spring means is engaging both of said abutment surfaces, said Belleville spring means is displaced to a point on said curve such that, when said plunger is engaged with said recess, said Belleville spring means will be displaced to said substantial threshold.
 19. The improvement as set forth in claim 18 wherein a stop surface is provided on said housing adjacent one of said abutment surfaces, and said stop surface is engaged by said Belleville spring means when said Belleville spring means is displaced to said substantial threshold.
 20. The improvement as set forth in claim 18 wherein said plunger and Belleville spring means constitute an assembly unit which may be removed from said housing.
 21. The improvement as set forth in claim 19 wherein said housing includes a tubular body having an opening through which a part of said plunger may project, and a removable end plug arranged to engage said body and having a face providing said stop surface. 